The prior art abounds with valves designed to, in one manner or another, sense and suppress unacceptably large surges or increases in the rate of flow of a fluid within a system--unacceptable, that is, in the sense of either surpassing an appropriate maximum flow rate at which a normal (or nearly so) mode of operation of the system may be maintained or, on the other hand, exceeding a flow rate considered to be a maximum that may be allowed from the standpoint of operational safety for the equipment, as well as for attending personnel.
However, these prior art valves are characterized, almost universally, by an "on-off" mode of operation, one in which the fluid flow therethrough is either substantially unimpeded or, in stark contrast, is actually terminated. In addition, a feature which proves a significant disadvantage in actual practice in many instances in the prior art, once the valve has sensed a surge and has reached a completely closed position, re-setting or opening the valve must be achieved manually, either at the valve itself (which may well be at some remote or otherwise inaccessible location) or by complete, and other expensive, shutdown of the associated system in order to remove the line pressure and release the closed valve.
Illustrative U.S. Pat. Nos. include 2,601,654-Wright and 2,179,144-Buttner, each of which discloses a valve which is spring-biased toward the open position to facilitate full fluid flow, but which is closed completely by an excessive increase in fluid flow or pressure in the line, opening again only upon removal of the increment of force of the fluid by some means external of the valve--no means are included within the valve for reducing the pressure differential and, as a result, permitting automatic reopening of the valve for allowing a re-establishment of normal operation.
A similar operation obtains in the drain valve of U. S. Pat. No. 2,136,898 - Thomas, in which liquid drain is effected through the normally open valve, which is then closed against a spring bias by incoming steam pressure.
An example of another type of valve by means of which regulation is achieved is U.S. Pat. No. 2,716,398 -McMullen, in which the valve member, in this instance, is normally fully closed by a biasing spring and oscillates or flutters between the positions of fully closed and fully open under the influence of an in order to regulate the vapor flow.